With conventional steering of boats with controllable propeller drives, a mechanical power transmission or mechanical power transmission connected to a hydraulic system is used for power amplification from a wheel to the propeller drive, an example of such a system being given in U.S. Pat. No. 5,399,112. This type of steering is well-suited for boats equipped with one drive, and for boats where the distance between the wheel and actuator for the controllable propeller drive is not such that the laying of cables between the wheel and actuator constitutes a problem.
For boats equipped with several drives and for boats where it is not desirable to have mechanical or hydraulic power transmission from the position where the wheel is located to actuators for setting the position of the propeller drives, it is expedient to utilize electronic control of the actuators. This applies in particular for a type of boat which is driven at planing speeds and is designed with a V-bottomed hull designed for planing, with an individually-controllable drive suspended on each side of the center line of the hull. These drives comprise an underwater housing projecting downwards from the outside of the hull, suspended in such way that it can be rotated in relation to the hull. A drive shaft is mounted in the underwater housing in such a way that it can rotate. The drive shaft drives a propeller shaft that is at least essentially horizontal, via a bevel gear mechanism contained in the underwater housing. Such a type of boat is known in, for example, SE-9402272-0. As the drives are suspended at right angles to the bottom of the hull on each side of the center line of the V-shaped hull, the drive shafts will be angled in relation to each other. This means that a mechanical power transmission for steering both drives would be very complex, in particular in the case when individual steering of the drives is required in response to movements of the wheel.
To achieve the abovementioned object, it is advantageous to utilize electronic control of steering for a propeller drive on a boat comprising a propeller drive suspended in a housing that can be rotated. In other types of boat, as well as in speedboats with planing V-bottomed hulls, it can be advantageous to utilize an electronic control system for the boat. This applies in particular when the boat comprises a plurality of power units in the form of propulsion motors and servo motors for direction setting devices, all of which are to be controlled by the helmsman and where it is desirable for the boat to be able to be driven in a plurality of modes, with the response from the throttle and wheel depending upon the mode in which the boat is being driven.
In order to ensure that the driving characteristics of the boat are retained when the degree of complexity of the boat increases, for example by several drives being utilized or by the boat being able to be controlled in a number of modes, support functions are required for the helmsman, for example in the form of mode selections for docking, operation at planing speeds, operation below planing speeds, acceleration characteristics, turning characteristics or operation in failsafe mode.